OFDM is used as a transmission technique for digital terrestrial broadcasting in Europe and Japan, wireless LAN, and the like. The OFDM technique is a method of performing modulation/demodulation by assigning data to a plurality of carriers orthogonal to each other. An Inverse Fast Fourier Transform (IFFT) process is performed in a transmitter, while a Fast Fourier Transform (FFT) process is performed in a receiver. Any modulation method can be employed with respect to each carrier, including QPSK (Quaternary Phase Shift Keying), QAM (Quadrature Amplitude Modulation), and the like.
When an antenna for receiving radio wave of digital terrestrial broadcasting or the like is installed, a position and an orientation of the antenna may be adjusted and optimized while observing a reception state of a receiver, i.e., a signal quality value of a received signal (see Patent Document 1 below). Also, the signal quality value of a received signal may be used for a control of AGC (Automatic Gain Control) for stabilizing a gain of a received signal selected by a tuner (see Patent Document 2 below).
In these cases, it is considerably important to provide a technique of detecting the signal quality value of a received signal using a predetermined measure. An example of such a technique of detecting the signal quality value of a received signal is disclosed in Patent Document 1.
Specifically, Patent Document 1 describes that an SP (scattered pilot) signal which is inserted every three carriers is used to detect an S/N value so as to detect a signal quality value (S/N value) corresponding to the reception quality of whole received data even when there is frequency selective interference, such as multipath interference or the like. Patent Document 1 also describes a technique of applying fluctuations in channel responses in a frequency direction and a time direction to correction of the S/N value so as to reflect on the S/N value a deterioration in bit error rate due to the fluctuation of the channel response, when there is multipath interference, reception is performed during moving, or the like. Patent Document 1 also describes a technique of correcting the S/N value, depending on the number of interfered carriers so as to detect an S/N value corresponding to the reception quality of whole received data, even when specific carriers in a received signal are interfered with.
Patent Document 3 below discloses an exemplary circuit which detects a fluctuation in channel response, depending on a frequency.
Patent Document 1: JP No. 2002-158631 A
Patent Document 2: JP No. 2001-102947 A
Patent Document 3: JP No. 2002-118533 A